// extract front part of string prior to searchString
function getFront(mainStr,searchStr){
		foundOffset = mainStr.indexOf(searchStr);
		if (foundOffset == -1) {
			return null;
		}
		return mainStr.substring(0,foundOffset);
}
// extract back end of string after searchString
function getEnd(mainStr,searchStr) {
		foundOffset = mainStr.indexOf(searchStr);
		if (foundOffset == -1) {
				return null;
		}
		return mainStr.substring(foundOffset+searchStr.length,mainStr.length);
}
// insert insertString immediately before searchString
function insertString(mainStr,searchStr,insertStr) {
		var front = getFront(mainStr,searchStr);
		var end = getEnd(mainStr,searchStr);
		if (front != null && end != null) {
				return front + insertStr + searchStr + end;
		}
		return null;
}
// remove deleteString
function deleteString(mainStr,deleteStr) {
		return replaceString(mainStr,deleteStr,'');
}
// replace searchString with replaceString
function replaceString(mainStr,searchStr,replaceStr) {
		var front = getFront(mainStr,searchStr);
		var end = getEnd(mainStr,searchStr);
		if (front != null && end != null) {
				return front + replaceStr + end;
		}
		return null;
}
